Method of making electrodes for electrochemical fuel cells

Abstract

In preparing a fluid diffusion electrode, typical methods include applying a catalyst ink to a fluid diffusion layer, drying the catalyst ink and hot-pressing the coated fluid diffusion layer to produce a fluid diffusion electrode. In the present application, unexpected improvements in the smoothness of the resulting electrode have been observed by drying the catalyst ink during compaction. To assist with drying the catalyst layer, the compacting step may be performed at elevated temperatures. In some embodiments, a release sheet may be applied to the catalyst layer prior to compaction. In addition or alternatively, partial drying of the catalyst layer may occur prior to compaction.

1 . A method for preparing a fluid diffusion electrode comprising: 
 providing a fluid diffusion layer;    applying a catalyst ink comprising catalyst particles and a solvent to the fluid diffusion layer to form a catalyst layer on the fluid diffusion layer; and    compacting the fluid diffusion layer and the catalyst layer until the catalyst layer has less than 8% solvent.    
     
     
         2 . The method of  claim 1  wherein the catalyst layer has less than 5% solvent after the compacting step.  
     
     
         3 . The method of  claim 1  wherein the compacting step is at elevated temperatures.  
     
     
         4 . The method of  claim 2  wherein the elevated temperatures are between 50 and 450° C.  
     
     
         5 . The method of  claim 2  wherein the elevated temperatures are between 140 and 160° C.  
     
     
         6 . The method of  claim 1  wherein the compaction step is for between 1 and 10 minutes.  
     
     
         7 . The method of  claim 1  wherein the compaction step is for between 4 and 7 minutes.  
     
     
         8 . The method of  claim 1  wherein the compaction step is between 5 and 100 bar.  
     
     
         9 . The method of  claim 1  wherein the compaction step is between 20 and 40 bar.  
     
     
         10 . The method of  claim 1  further comprising partially drying the catalyst layer prior to the compacting step.  
     
     
         11 . The method of  claim 10  wherein the partially drying step comprises drying the catalyst layer in air.  
     
     
         12 . The method of  claim 11  wherein the partially drying step is for 6 minutes or less.  
     
     
         13 . The method of  claim 1  wherein the applying step is performed with a knife coater.  
     
     
         14 . The method of  claim 1  further comprising applying an ionomer solution to the catalyst layer prior to the compacting step.  
     
     
         15 . The method of  claim 1  further comprising applying a release sheet to the catalyst layer prior to the compacting step.  
     
     
         16 . The method of  claim 15  wherein the porosity of the release sheet is less than the porosity of the fluid diffusion layer.  
     
     
         17 . The method of  claim 15  wherein the release sheet comprises at least one of polytetrafluoroethylene, amorphous thermoplastic polyetherimide, polyvinylidene fluoride, THV impregnated paper, or PE.  
     
     
         18 . The method of  claim 15  wherein the release sheet comprises polytetrafluoroethylene sheets.  
     
     
         19 . The method of  claim 15  further comprising removing the release sheet after the compacting step.  
     
     
         20 . The method of  claim 1  wherein the compacting step produces a first fluid diffusion electrode, the method further comprising: 
 providing an ion-exchange membrane;    providing a second fluid diffusion electrode; and    bonding the first fluid diffusion electrode, the ion-exchange membrane and the second fluid diffusion layer together to form a membrane electrode assembly.    
     
     
         21 . The method of  claim 20  wherein the providing a second fluid diffusion layer comprises: 
 providing a second fluid diffusion layer;    applying a second catalyst ink to the second fluid diffusion layer to form a second catalyst layer on the second fluid diffusion layer; and    compacting the second fluid diffusion layer and the second catalyst layer until the second catalyst layer has less than 8% solvent.